1. Field of the Invention
The present invention relates to a spin-valve type thin film element in which electrical resistance changes in response to the relationship between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is influenced by an external magnetic field. More particularly, the invention relates to a spin-valve type thin film element in which a relative angle between the magnetization of a pinned magnetic layer and the magnetization of a free magnetic layer can be properly adjusted.
2. Description of the Related Art
FIG. 7 is a sectional view of a spin-valve type thin film element (spin-valve type thin film magnetic head) which detects a recording magnetic field from a recording medium such as a hard disk drive.
This spin-valve type thin film element includes an antiferromagnetic layer 10, a pinned magnetic layer 11, a non-magnetic electrically conductive layer 12, and a free magnetic layer 13 deposited in that order, and hard magnetic bias layers 5 and 5 formed on both sides thereof.
Generally, a nickel--manganese (Ni--Mn) alloy film is used for the antiferromagnetic layer 10, a nickel--iron (Ni--Fe) alloy film is used for the pinned magnetic layer 11 and the free magnetic layer 13, a copper (Cu) film is used for the non-magnetic electrically conductive layer 12, and a cobalt--platinum (Co--Pt) alloy film or the like is used for the hard magnetic bias layers 5 and 5. Numerals 6 and 7 represent an under layer and a protective layer, respectively, composed of a non-magnetic material such as tantalum (Ta).
As shown in the drawing, the antiferromagnetic layer 10 and the pinned magnetic layer 11 are formed in contact with each other, the pinned magnetic layer 11 is put into a single domain state in the Y direction by an exchange anisotropic magnetic field caused by exchange coupling at the interface between the pinned magnetic layer 11 and the antiferromagnetic layer 10, and the magnetization direction is fixed in the Y direction. The exchange anisotropic magnetic field occurs at the interface between the antiferromagnetic layer 10 and the pinned magnetic layer 11 by film deposition or annealing while applying the magnetic field in the Y direction.
Also, the magnetization direction of the free magnetic layer 13 is aligned in the X direction under the influence of the hard magnetic bias layers 5 and 5 which are magnetized in the X direction.
In the spin-valve type thin film element, a sensing current is applied from electrically conductive layers 8 and 8 formed on the hard magnetic bias layers 5 and 5 into the pinned magnetic layer 11, the non-magnetic electrically conductive layer 12, and the free magnetic layer 13. The driving direction of a recording medium such as a hard disk drive is in the Z direction, and if a leakage magnetic field from the recording medium is applied in the Y direction, the magnetization of the free magnetic layer 13 changes from the X direction to the Y direction. Because of the relationship between the change in the magnetization direction in the free magnetic layer 13 and the pinned magnetization direction of the pinned magnetic layer 11, the electrical resistance changes, and the leakage magnetic field from the recording medium is detected by the voltage change based on the change in the electrical resistance.
Although the hard magnetic bias layers 5 and 5 are formed to put the free magnetic layer 13 into a single domain state and align the magnetization in the X direction shown in the drawing, the magnetization of the free magnetic layer 13 is not always aligned in the X direction in the entire region when a sensing current is applied.
Japanese Patent Publication No. 9-92907 (page 2, column 2, line 14) describes that "in the magnetoresistive element, the first ferromagnetic layer 21 is subjected to a magnetic field caused by static magnetic coupling with the second ferromagnetic layer 23, a magnetic field caused by exchange coupling between layers, and an electric current magnetic field." The "first ferromagnetic layer 21" corresponds to the free magnetic layer 13 shown in FIG. 7, and the "second ferromagnetic layer 23" corresponds to the pinned magnetic layer 11 shown in FIG. 7.
The above Patent Publication also has the following description (page 2, column 2, line 23). "However, each magnetic field essentially has a different distribution of height directions, and thus, complete offset cannot be performed. For example, FIG. 3A is a graphic representation showing the distribution of height directions with respect to the static magnetic field caused by static magnetic coupling, the electric current magnetic field and the magnetization in the first ferromagnetic layer. As is clear from the drawing, since the static magnetic field caused by static magnetic coupling and the electric current magnetic field are properties oriented in the same direction in relation to the vertical axis, the two magnetic fields cannot be offset uniformly, the height component of the magnetization of the first ferromagnetic layer crosses zero at both ends in the height direction. Thereby, magnetic domain walls are produced, which may lead to Barkhausen noise."
That is, as shown in FIG. 9, even when the static magnetic field caused by static magnetic coupling and the electric current magnetic field caused by a sensing current are offset with respect to the magnetization C2 in the central region in the Y direction (height direction) in the free magnetic layer 13, magnetizations C1 and C3 in end regions in the Y direction are inclined in relation to the X direction.
As described above, the free magnetic layer 13 has a distribution of different magnetization directions in relation to the Y direction under the influence of the static magnetic field caused by static magnetic coupling and the electric current magnetic field caused by a sensing current.
Therefore, as shown in FIG. 9, the relative angle between magnetizations C1 and C3 of the free magnetic layer 13 and the magnetization D of the pinned magnetic layer 11 is not set at 90.degree., and thus, asymmetry deteriorates. The word "asymmetry" means the vertical asymmetry of the regenerated output waveform.
In Japanese Patent Publication No. 9-92907, an attempt is made to set at 90.degree. the relative angle between the magnetization of the first ferromagnetic layer (free magnetic layer) and the magnetization of the second ferromagnetic layer (pinned magnetic layer), as described in the following (page 3, column 3, line 17). "FIG. 3B shows the distribution of height directions with respect to the static magnetic field caused by static magnetic coupling, the electric current magnetic field and the magnetization in the first ferromagnetic layer 1. In this distribution, the static magnetic field caused by static magnetic coupling and the electric current magnetic field are properties standing opposed to each other in relation to the vertical axis. Also, since the magnetization of the first ferromagnetic layer 1 is directed at 45.degree. in relation to the direction of the applied magnetic field, the magnetic fields are added, and thus, the first ferromagnetic layer 1 has substantially uniform height components of the magnetization in relation to the height direction."
That is, as shown in FIG. 10, the magnetization D of the second ferromagnetic layer (pinned magnetic layer 11) is fixed, being inclined by .theta.2 (=45.degree.) in relation to the Y direction, and because of static magnetic coupling with the pinned magnetic layer 11, the magnetization C2 of the first ferromagnetic layer (free magnetic layer 13) is inclined by .theta.2 (=45.degree.). The relative angle between magnetizations C1, C2, and C3 of the free magnetic layer and the magnetization D of the pinned magnetic layer is adjusted to 90.degree., and thus, the static magnetic field and the electric current magnetic field are offset.
Japanese Patent Publication No. 9-92907 aims to overcome the problem of asymmetry by the method described above.
However, it has been confirmed that the magnetization of the free magnetic layer 13 in the central region has a different direction from that in end regions in relation to the track width direction (X direction). The magnetization state is shown in FIG. 8.
As shown in FIG. 8, magnetizations A and B in end regions of the free magnetic layer 13 are easily aligned in the X direction. The reason is that the end regions of the free magnetic layer abut on hard magnetic bias layers 5 and 5, and are strongly influenced by the bias magnetic field of the hard magnetic bias layers 5 and 5 in the X direction.
In accordance with Japanese Patent Publication No. 9-92907, although the relative angle between magnetizations C1, C2, and C3 in the central region of the free magnetic layer 13 and the magnetization D2 of the pinned magnetic layer 11 can be set at 90.degree. or its approximation, since magnetizations D1, D2, and D3 of the pinned magnetic layer 11 are fixed so as to be inclined in relation to the Y direction, the relative angle between magnetizations A and B in end regions of the free magnetic layer 13 and magnetizations D1 and D3 of the pinned magnetic layer 11 cannot be set at 90.degree., resulting in the deterioration of asymmetry in the end regions.
The deterioration of asymmetry in the end regions makes it difficult to detect the track position accurately, and easily leads to a servo error.